MediaLab v2006-v2008 continues to be running ok in most cases on Vista with the exception of some video issues we're still trying to work out. With respect to DirectRT, we have a couple options to offer--we have an alpha version of DirectRT for Vista you can try--but it's new and we're still working out some issues. You can use it now and we will continue to fix any bugs that come up over the coming months.
The other option (see above) would be to install XP on your systems--you ought to be able to do this as a "dual boot" setup where Vista is left intact and you simply choose which version of Windows you want when you start the system. That way you could use the standard v2008 XP version of DirectRT without voiding your warranty (unless it states otherwise, of course).